Internal combustion engines are provided with a supply of lubricating oil in order to reduce friction between moving parts of the engine. Once the lubricating oil reaches a given level of dilution or contamination (e.g., from fuel, water, soot, or other products), the engine is serviced to remove the oil from the oil sump and replace the oil with fresh oil. However, such maintenance is expensive and time-consuming. Further, if an operator continues to operate the engine with the diluted/contaminated oil, engine degradation may occur. Thus, it may be desirable to prolong the duration between oil change events.
U.S. Pat. No. 5,238,085 A discloses an oil changing system for a diesel engine, in which an oil level in an oil sump of the diesel engine is monitored and, if the oil level drops below a predetermined limit value, fresh oil, which is stored in a separate oil tank, is automatically introduced into the oil sump. In addition, after a predetermined operating time of the diesel engine or if a certain degree of soiling of the oil present in the oil sump is detected, the oil present in the oil sump and in the oil tank may be recirculated in an oil circuit comprising the oil sump, the oil tank and oil lines connecting the oil sump and the oil tank to each other, wherein an oil filter for cleaning the oil is arranged in an oil line.
JP 2012 137 055 A relates to a method for regenerating an oil present in an oil sump, according to which a degree of soiling of the oil is detected by means of sensors and fresh oil from an oil tank is supplied to the oil sump if the degree of soiling of the oil exceeds a predetermined limit value.
However, the inventors herein have recognized issues with the above approaches. The use of a separate oil tank may add cost and complexity to the engine system. Further, approaches that rely on a predetermined operating time may not take into account variation of oil dilution that may occur during different engine operating conditions. For example, certain engine operating conditions, such as soot particle filter regenerations, may result in a higher degree of fuel being present in the oil.
A soot particle filter with which combustion gases of a diesel engine are filtered in order to reduce the particle emission of the diesel engine is customarily arranged in an exhaust tract of the diesel engine. The particles filtered out of the exhaust gas are stored in the soot particle filter. The loading of the soot particle filter with particles causes the generation of an exhaust gas counter pressure which limits the power of the diesel engine. If an exhaust emission of the diesel engine is too greatly obstructed by the exhaust gas counter-pressure, the soot particle filter has to be regenerated. For this purpose, use is made of a regeneration operation by means of which the particles stored in the soot particle filter are burned. The power of the diesel engine is not impaired by carrying out a regeneration operation.
In a regeneration operation, in particular soot particles are converted into carbon dioxide. Such a regeneration operation is carried out by an engine control device depending on an operating profile of the diesel engine. If the diesel engine is severely loaded or operated in a high power range, relatively high exhaust gas temperatures occur that may lie within the range of the particle combustion temperature to be used for the regeneration, and therefore the soot particle filter is automatically regenerated during the operation of the diesel engine. By this means, the time interval between regeneration operations to be carried out is extended, or a regeneration operation is not required. If, by contrast, the diesel engine is operated predominantly in a low power range, relatively low exhaust gas temperatures occur in which no combustion of the particles takes place. The soot particle filter will then continue to be loaded further with particles, and therefore the regeneration operations have to be carried out at relatively short intervals.
A high exhaust gas temperature is therefore required in order to carry out a regeneration operation. Various techniques are known in order to achieve this. One of said techniques is the late post-injection of the fuel, in which the fuel is injected into the cylinder of the diesel engine during the expansion of the combustion cycle. The late post-injection is associated with poor efficiency of the combustion of the fuel, as a result of which the exhaust gas temperature rises.
During the late post-injection of the fuel into the cylinder, a portion of the fuel evaporates in the cylinders instead of being burned. Some of the evaporated fuel is deposited here on the cylinder walls. The unburned fuel adhering to the cylinder walls may pass the piston rings in the direction of the crankshaft during the piston movements and thereby enter an oil sump of the crank case. By this means, the oil located there is diluted, which impairs the quality of the oil and in particular makes the lubricating action thereof worse. The occurrence of this engine oil dilution is reinforced by an admixture of biofuels. In order not to increase the wear of the diesel engine and not to impair the durability thereof, maintenance intervals at which an oil change takes place have to be reduced.
The inventors herein propose a system and method to extend oil changing intervals in a diesel engine, wherein the diesel engine has at least one soot particle filter. In one example, an oil system for a diesel engine, in particular of a motor vehicle, may include at least one oil chamber forming an oil sump, at least one oil reservoir which is arranged separately from the oil chamber, and is at least partially arranged at the same geodetic height as the oil chamber, at least one fluid connection which connects the oil chamber to the oil reservoir in a communicating manner and on which at least one electrically operable shut-off unit is arranged, wherein the shut-off unit blocks the fluid connection in a blocking state and at least partially releases the same in a release state, and at least one electronic unit which is connectable in terms of signaling to the shut-off unit and may detect a number of regeneration operations carried out for regenerating the soot particle filter, for estimating an instantaneous degree of dilution of an oil present in the oil chamber taking into consideration the number of regeneration operations carried out and for activating the shut-off unit depending on the estimated, instantaneous degree of dilution of the oil present in the oil chamber.
In one example, an instantaneous degree of dilution of the oil present in the oil chamber may not be determined via a sensor arrangement arranged on the oil chamber, but rather estimated by means of the electronic unit taking into consideration the respective number of regeneration operations carried out for regenerating the soot particle filter. This makes a more cost-effective and lighter weight refinement of the oil system possible. If the estimated instantaneous degree of dilution of the oil present in the oil chamber is smaller than or equal to a predetermined limit value greater than zero, the shut-off unit is held in the blocking state thereof, which corresponds to a normal state of the shut-off unit which the latter takes up or maintains preferably without activation by the electronic unit. If the estimated, instantaneous degree of dilution of the oil lies above the predetermined limit value, the shut-off unit is at least temporarily transferred from the blocking state thereof into the release state thereof by means of the electronic unit. By this means, the oil which is present in the oil chamber and is diluted with diesel fuel by regeneration operations which are carried out may be mixed with oil present in the oil reservoir, as a result of which the actual degree of dilution of the oil present in the oil chamber is reduced. By this means, in comparison to an operation without thorough mixing of the oils, the oil present in the oil chamber and in the oil reservoir has to be exchanged for fresh oil only at a later time. Consequently, with the oil system, oil changing intervals are extended in the case of a diesel engine which has at least one soot particle filter.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.